Integrated Photonic Nonreciprocal Devices Based on Susceptibility‐Programmable Medium

Abstract The switching and control of optical fields based on nonlinear optical effects are often limited by relatively weak nonlinear susceptibility, which requiring strong optical pump fields. Here, an optical medium with programmable susceptibility tensor based on polarizable atoms is proposed. Under a structured optical pump, the population of atoms in the ground state could be efficiently controlled by tuning the chirality and intensity of optical fields, and thus the optical response of the medium is programmable in both space and time. The potential of this approach is demonstrated by engineering the spatial distribution of the complex susceptibility tensor of the medium in photonic structures, which enables the realization of nonreciprocal optical effects. Specifically, the advantages of chiral interaction between atoms and photons are investigated in an atom‐cladded waveguide, theoretically showing that strong, rapidly switchable, and reconfigurable isolation of optical signals in a selected optical mode is possible. The susceptibility‐programmable medium provides a promising way to efficiently control the optical field, opening up a wide range of applications for integrated photonic devices and structured optics.